I have met such issue with outlook 2007, even without using SyncToy to syncing the .pst file. My problem caused by I do not have enough space to hold the outlook files.
Not very sure yours. But could stable repro this after syncing with synctoy?
If you resolve the outlook could not open issue by re-open outlook, then you close outlook(release the accessing using to outlook.pst file), then run synctoy 2.1, what happen? Could you run successfully? After runing the syncing try to open outlook, have a try if there is still this problem.
Thanks,
Ping
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